On exposition: like everything else in writing, it's a tension, and a line that you will wobble back and forth over a thousand times while you learn your craft.
First you will not explain enough. Then you will overcorrect and explain too much. Then, you will become enamored of your own cleverness, and become cryptic and mysterious. Then you will become frustrated by the rejections that read "This is beautifully written, but too ambiguous," and you will over-explain. Then you will under-explain. Then you will over-explain and your first reader will say, "but this is boring." Then you will under-explain... and you will sell something. And then you will not sell anything else for a while, and then you will over-explain and sell something. You will bemoan your fate. You will bemoan the stupidity of editors, or their fickleness.
You will sell a novel. Readers will be confused. You will sell another novel. Your editor will say, "I'm confused." You will spend a month and a half clarifying the obvious.
Readers will still be confused.
You will bemoan the stupidity of readers, or their fickleness.
You will over-explain. You will under-explain. You will put in a bunch of exposition your editor asked for and then on the CEM take half of it out again.
Finally, more people than not will understand.
Thanks to Random Walk Writer for the link. Would that I can continue to confuse people AFTER I sell something! Now I'm confusing without the right! However, the yo-yo struggle is familiar even so.